A bumper serving as an impact absorbing mechanism is equipped in the front and rear portions of the motor vehicle for absorbing and cushioning the impact generated at a time of being collided with or brought into contact with the other motor vehicle or the other body. Further, a bumper formed by bending a steel plate is used as a conventional bumper. However, in recent years, in proportion as a demand level against a car styling becomes higher, and a performance improvement on a safety and a grace of an outer shape are pursued, a bumper which is matched to a body styling in view of a shape, a color and the like is going to be demanded.
The bumper mentioned above is structured such that the bumper is covered with a bumper facia made of thermoplastic plastics, and an impact absorbing member is arranged in an inner portion thereof. The bumper facia is formed by injection molding or stamping a polypropylene or the other thermoplastic plastics. In recent years, there has been proposed a polymer alloy obtained by adding the polypropylene to the other composite resin, taking into consideration a recycle performance at a time of disposing a motor vehicle. Further, the impact-absorbing member employs various aspects in view of a performance and a cost, however, employs an aspect centering on a bumper beam as a general aspect.
As the bumper beam, in conventional, there has been frequently employed a structure formed by bending a steel plate as disclosed in Japanese Patent Application Laid Open (JP-A) No. 6-255433 and JP-A No. 6-328988, however, a synthetic resin bumper beam reinforced by a fiber group such as a glass fiber, a carbon fiber or the like starts being used as disclosed in JP-A No. 6-344837, JP-A No. 11-34140 and JP-A No. 2-299947.
It is a mainstream that the bumper beam is coated with a bumper facia in a surface thereof, however, a foam body for absorbing an energy may be interposed between the bumper beam and the bumper facia as disclosed in Japanese Utility Model Application Laid Open (JP-U) No. 56-103349 and JP-U No. 57-32555.
Further, in accordance with a new proposal, there is a blow molded bumper serving as a structure doubling as the bumper facia and the bumper beam by doing away with the bumper facia (JP-A No. 4-62029, JP-A No. 5-116572, Japanese Patent Application Publication No. 2-46418, JP-U No. 58-194942 and the like).
There is a proposal that the blow molded bumper is reinforced by a bumper beam as disclosed in Japanese Utility Model Application Publication No. 4-33165.
The conventional bumper system mentioned above can absorb and cushion an energy caused by a high impact value (20 kN or higher) at a time of being collided with and brought into contact with the other motor vehicle or the other body, however, it is hard to absorb and cushion the energy caused by a low impact value (5 kN or lower).
Further, there is described in JP-A No. 2002-187508 a structure having a hollow portion, integrated by forming concave ribs from a front surface wall and a back surface wall and bonding leading end portions thereof, and planning to improve an impact absorbing performance. Further, there is described in Japanese Patent No. 3313999 an impact-absorbing member for a vehicle structured by a polypropylene resin having an elastic modulus in bending of 5000 kg/cm2 to 2500 kg/cm2.
In this case, a duct for a vehicle forming a concave rib and a plate-like rib and having an impact absorbing performance is described in JP-A No. 2000-193057 and JP-A No. 2001-239573, a duct for a vehicle inserting a reinforcing core material and having an impact absorbing performance is described in JP-A No. 2001-34156, and a bumper reinforcement having a concave rib and a plate-like rib is described in Japanese Patent No. 2714567.
As the impact absorbing member for the vehicle described in JP-A No. 2002-187508 and Japanese Patent No. 3313999, the structure integrated by forming the concave rib from the front surface wall and the back surface wall of a hollow double wall structure body made of a thermoplastic resin and bonding the leading end portions to each other can secure a desired impact absorbing amount if a thickness of the hollow body is made sufficient, however, the desired impact absorbing amount can not be obtained in the case that the thickness of the hollow body is limited such as the case a space between the bumper facia and the bumper beam is little on styling, and it is required to improve the impact absorbing performance just after the impact is applied.
Accordingly, an object of the present invention is to obtain an impact absorbing member of a motor vehicle which can correspond to an energy caused by a low impact value (5 kN or lower, in particular between 3 kN and 5 kN) as well as absorbing an energy caused by a high impact value (20 kN or higher) at a time of being collided with and brought into contact with the other motor vehicle or the other body, can secure a desired impact absorbing performance even in the case that a thickness of an impact absorbing member or a hollow body is limited, is particularly excellent in an impact absorbing performance just after an impact is applied, and is excellent in a functionality and a styling characteristic which can maintain a high impact absorbing performance, by depressing a first wall of the hollow body toward an opposing second wall and depressing the second wall toward the opposing first wall so as to form a plurality of one concave ribs and a plurality of the other concave ribs, integrally welding leading end portions of the one concave ribs and the other concave ribs to each other, further protruding the first wall toward the opposing second wall and protruding the second wall toward the opposing first wall so as to form a pair of plate-like ribs constituted by one plate-like rib and the other plate-like rib in such a manner as to connect a plurality of concave ribs, and integrally welding leading end portions of the one plate-like rib and the other plate-like rib to each other.